This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-368271, filed Dec. 24, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a backlight unit for use in a planer display represented by a liquid crystal display device, and more particularly to a backlight unit comprising rubber holders.
In recent years, planar displays represented by a liquid crystal display are used as TV displays, computer displays, car-navigation system displays and the like. This is because they are thin and light and consume but a little power.
A liquid crystal display, for example, comprises a light-transmitting liquid crystal display panel, a backlight unit, and a frame and a bezel, in most cases. The liquid crystal display panel comprises a pair of parallel substrates and a liquid crystal layer held between the substrates. The backlight unit is arranged on one surface of the liquid crystal display panel. The bezel made of metal is secured to the frame that is made of resin. The display panel and the backlight unit are mounted on the frame, partly held between the bezel and the frame. The liquid crystal display further comprises a drive circuit board for supplying drive signals to the panel. The drive circuit board is mounted on the frame, opposing the back of the backlight unit so as to reduce the width of the peripheral portion of the display device, that is, the with of the bezel.
Most backlight units comprise a light guide plate, a tubular light source, and a reflecting plate. The light guide plate is made of acrylic resin. One of the light guide plate serves as light-emitting surface. The tubular light source is positioned, extending along one side of the light guide plate. The reflecting plate covers the tubular light source. Light-scattering member is printed or provided on the back of the light guide plate. This member is made of acrylic resin, i.e., the same material as the light guide plate. The ends of the tubular light source are connected to a connector through cables, respectively.
A heat-shrinkable tube is fitted on the junction between each cable and an end of the light source. Further, two holders made of rubber are mounted on the end portions of the light source, respectively. Each holder covers the junction between one cable and one end of the light source is mounted on each end portion.
In the backlight units, the cables are led toward one side of the tubular light source. One cable, for example, the low-voltage cable, is inevitably bent at the part near the junction. A stress may likely be imposed on the bent part of the cable, impairing the electrical connection between the cable and the light source. Consequently, the tubular light source will fail to emit sufficient light or will emit smoke. Further, the sheath of the cable may be broken at the bent part, due to the stress applied on the bent part. Persons who repair the backlight unit may suffer from electric shocks.
The junction between each cable and an end of the light source must not be exposed. To this end, a heat-shrinkable tube is mounted on the junction. This decreases the productivity of the backlight unit and, ultimately, raises the price thereof.
The present invention has been made in view of the foregoing and its object is to provide a backlight unit in which insufficient electrical connection is prevented and the number of components is decreased and which, therefore, excels in productivity and operating reliability.
To attain the object, a backlight unit according to the invention comprises: a light guide plate that is almost rectangular: a tubular light source arranged at one side of the light guide plate; a frame supporting the light guide plate and the tubular light source; connection cables connected to ends of the tubular light sources; and holders made of elastic material and mounted on junctions, each between an end part of one tubular light source and one connection cable. Each of the holders comprises a main body and hollow cylindrical extensions formed integral with the main body and extending therefrom. The main body has a hole in which an end part of the tubular light source is fitted. Each extension has a hole communicating with the hole of the main body. One end of each connection cable is inserted in one extension, and each extension directly covers one end part of a connection cable.
In the backlight unit, the holders reduce the stress on the junctions between the tubular light source and the end parts of the connection cables. This prevents the connection cables from being disconnected from the light source and insufficient electrical connection between the cables and the light source. Hence, the backlight unit can have its operating reliability enhanced. Further, since the holders are made of elastic material and flexible, the connection cables can be easily bent even though they are covered by the holders. Moreover, the holders are more durable than the conventional coatings and are hardly broken, thus preventing those people who repair the backlight unit from suffering from electric shocks. In addition, a heat-shrinkable tube need not be used as in the conventional backlight unit. This helps to increase the productivity of the backlight unit and, ultimately, to lower the manufacturing cost of the backlight unit.
Another backlight unit according to the invention comprises: a light guide plate that is almost rectangular; a tubular light source arranged at one side of the light guide plate; a frame supporting the light guide plate and the tubular light source; connection cables connected to ends of the tubular light sources; and holders made of elastic material and mounted on junctions, each between an end part of one tubular light source and one connection cable. Each of the holders comprises a main body and hollow cylindrical extensions formed integral with the main body and extending therefrom. The main body has a hole in which an end part of the tubular light source is fitted, and each extension has a hole communicating with the hole of the main body. One end of each connection cable is inserted in one extension, each extension directly covers one end part of a connection cable. Each of the connection cables has wires and a sheath covering the wires. The end of the sheath of each connection cable is located closer to the main body of one holder than to a junction between main body and the extension.
In this backlight unit, the junction between the main body and extension of each holder, i.e., the bent part of the holder, is spaced apart not only from the wires of the of the connection cables. Hence, the holders reduce the stress applied at the junction between the tubular light source and one connection cable, and the stress applied on the wires of each connection cable. This prevents the cables from being disconnected from the light source and insufficient electrical connection between the cables and the light source. The backlight unit can have its operating reliability enhanced.
As described above, the present invention can provide a backlight unit in which insufficient electrical connection is prevented and a small number of components are provided and which, therefore, excels in productivity and operating reliability.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.